Duct wall and reverse flow combustor incorporating same

ABSTRACT

A reverse flow combustor, as used in a gas turbine engine, is described. The combustor comprises inner and outer curl members which define the discharge flow path for the hot gas stream generated in the combustion zone of the combustor. This annular flow path curves inwardly through approximately 180* for discharge of the hot gas stream to the turbine of the engine. The outer curl member comprises a pair of spaced plates which define chamber means through which cooling air is flowed to reduce the metal temperature of the curl member. The metal plates are spaced apart by dimples to assure the desired mass flow of cooling air at all times. One embodiment illustrates a single chamber for the flow of cooling air. Another embodiment includes an intermediate plate which defines first and second chambers through which cooling air is flowed. Other features of the invention are described which accommodate thermal growth differentials encountered in operation of the engine.

Mat to [451 Oct. 29, 1974 DUCT WALL AND REVERSE FLOW COMBUSTOR INCORPORATING SAME [75] Inventor: Lawrence R. Matto, Huntington,

Conn.

[73] Assignee: Avco Corporation, Stratford, Conn.

[22] Filed: Sept. 6, 1972 [21] Appl. No.: 286,720

[52] US. Cl 60/3932, 60/3966, 60/3936 [51] Int. Cl. F02c 3104, F020 7/ 18, F02c 7/20 [58] Field of Search 60/3965, 39.66, 39.32,

[56] References Cited UNITED STATES PATENTS 2,080,425 5/1937 Lysholm 60/3936 X 2,591,676 4/1952 Clayton 60/3932 X 2,692,478 10/1954 Hill 60/3932 UX 2,958,194 ll/l960 Bayley 60/3965 3,228,190 l/l966 Brown 60/3936 X 3,284,048 11/1966 Tumavicus.. 415/178 3,333,414 8/1967 Saintsbury 60/3969 X 3,545,202 12/1970 Batt et al. 60/3965 3,570,241 3/1971 Alexander 60/3965 3,645,081 7/1953 McDonald 60/3971 X 3,652,181 3/1972 Wilhelm 60/3966 3,670,497 6/1972 Sheldon 60/3932 Primary Examiner-C. J. Husar Assistant Examiner-Robert E. Garrett Attorney, Agent, or Firm-Charles M. Hogan; Gary M. Gron [57] ABSTRACT A reverse flow combustor, as used in a gas turbine engine, is described. The combustor comprises inner and outer curl members which define the discharge flow path for the hot gas stream generated in the combustion zone of the combustor. This annular flow path curves inwardly through approximately 180 for discharge of the hot gas stream to the turbine of the engine. The outer curl member comprises a pair of spaced plates which define chamber means through which cooling air is flowed to reduce the metal temperature of the curl member. The metal plates are spaced apart by dimples to assure the desired mass flow of cooling air at all times. One embodiment illustrates a single chamber for the flow of cooling air. Another embodiment includes an intermediate plate which defines first and second chambers through which cooling air is flowed. Other features of the invention are described which accommodate thermal growth differentials encountered in operation of the engine.

PATENTEDHBTZQ 1914 v 3.8441 16 DUCT WALL AND REVERSE FLOW COMBUSTOR INCORPORATING SAME The present invention relates to improvements in ducts for defining the flow path of high temperature fluid streams and more particularly to reverse flow combustors of gas turbine engines.

The field of gas turbine engines faces a particular challenge in providing ducts for high temperature gas streams. This is most true in gas turbine engines employed in the propulsion of aircraft where both extreme high temperatures and high weight construction are necessary to economically achieve desired levels of performance. Beyond this, there are also operational hazards such as vibration and extreme G loadings.

Beyond the general problem of ducting high temperature gas streams is such engines, a more specific problem is encountered in so-called reverse flow combustors. Such combustors, which are advantageous in minimizing overall engine weight and bulk, have an entrance end remote from the engine's compressor. Air for combustion enters the combustor and travels in reverse fashion through the combustion zone in the generation of a hot gas stream. This hot gas stream is then turned inwardly through 180 to the turbine assembly of the engine. Turning of this gas stream is accomplished by a U" shaped annular passageway commonly referenced as a curl assembly comprising of an inner and outer curl members. The outer curl member, or duct wall, is particularly subject to extreme temperatures, which can be highest in the engine. The outer curl member thus has presented particular problems in providing a combustor which is not only serviceable but also economically provides an adequate service life.

While there have been many proposals to cool duct members in general and the curved duct members of such combustors, as well, none is fully satisfactory in all respects of economy and service life. To explain these prior proposals further, it is a well known expedient to bleed relatively cool air from an engines compressor and impinge or otherwise flow this cooling air over the duct walls, and other structures, of the engine which are subject to elevated temperatures. Also cooling air may be derived from sources other than the engine compressor.

Where compressor air is utilized for cooling, a primary consideration is that the mass of cooling air be minimized since it represents a decrement to the overall cycle efficiency of the engine. This leads to the necessity of devising cooling arrangements which provide a high degree of cooling efficiency incorporated into a structure which is compatable with the other require ments of the operating environment of the engine.

Accordingly, one objection of the invention is to provide an improved duct wall construction for defining the flow path of a hot fluid stream.

Another object of the invention is to provide such a duct wall for guiding the gas stream along a curved flow ath.

p Another object of the invention is to provide an improved reverse flow combustor characterized by an outer curl member capable of withstanding extreme elevated temperature and providing a prolonged and improved service life.

The above ends, in accordance with the broader aspects of the invention, are attained by a duct wall comprising of a pair of spaced plates defining chamber means therebetween. One of these plates is exposed directly to a hot gas stream. Means are provided for introducing cooling air between these plates and flowing the cooling air over substantially the entire surface area of the plate which is exposed to the hot gas stream. Further, spacing means, advantageously in the form of dimples, are provided to maintain a minimum spacing between the plates so as to assure a desired flow of cooling air at all times.

The spaced plates of the duct wall may form a single chamber with cooling air being introduced into one end and then discharged from the other end into the hot fluid stream. Even greater cooling effectiveness may be obtained by providing an intermediate plate which defines first and second chambers, again cooling air is introduced into one end of each of these chambers and then discharged back into the hot fluid stream.

This duct assembly may be incorporated into a reverse flow combustor which includes inner and outer lines defining a combustion zone. Inner and outer curl members form respective extentions of these liners and define an annular flow path for the gas stream which curves inwardly through approximately for discharge of the gasstream to the turbine of an engine. The outer curl member is formed of two spaced plates which define chamber means through which cooling air is passed. The plates may define a single chamber or more advantageously an intermediate plate may be provided to define first and second chambers for the flow of cooling air. Provision is also made in the mounting of the intermediate plate as well as in mounting of the outer curl assembly itself for differential thermal growth of the components of the outer curl member.

The above and other related objects and features of the invention wll be apparent from a reading of the following description, with reference to the accompanying drawings, and the novelty thereof pointed out in the appended claims.

In the drawings:

FIG. 1 is a partial view, in longitudinal section, of a gas turbine engine, particularly illustrating a reverse flow combustor embodying the present invention;

FIG. 2 is an enlarged longitudinal section of a portion of the reverse flow combustor seen in FIG. 1;

FIG. 3 is a section similar to FIG. 2 illustrating another embodiment of the invention;

FIG. 4 is a view taken on line IV-IV on FIG. 2 and FIG. 5 is a view taken on line V-V in FIG. 3.

FIG. 1 illustrates portions of a gas turbine engine. It includes the final stages of an axial flow compressor 10 which pressurizes air for supporting combustion of fuel in the generation of a motive fluid stream. Air discharged from the compressor 10 flows through a diffuser l2 and then outwardly and rearwardly along passageway 14 toward a reverse flow combustor 16. The combustor'l6 may be of the annular type comprising inner and outer annular liners 18 and 20 which are respectively spaced from a turbine casing 22 and engine house 24.

Air discharged from the compressor 10 flows, from the passageway 14, through the annular spaces between the liners and their adjacent casings toward the remote, or entrance, end of the combustion chamber which is defined by the liners l8 and 20. This air enters the combustion chamber and supports combustion of fuel injected by nozzles 26, in known fashion, to generate a hot gas stream. This hot gas stream then flows, in reverse fashion, back, generally, towards the compressor l and is then turned inwardly through 180 degrees by inner and outer curl members 28 and 30, which are connected to and represent extensions of the liners l8 and 20. After being turned by the curl members 28 and 30, the hot gas stream is discharged through a nozzle diaphragm 32 to a turbine 34, which is connected to and drives the compressor 10. The hot gas stream may then be directed to and drive a power turbine 36. The power turbine 36 is provided with a power take-off shaft (not shown) which can be connected to whatever mechanism it is desired to drive, as for example, the rotor of a helicopter.

Referencing next FIG. 2, it will be seen that the outer curl member 30 is compositly formed by spaced, sheet metal plates 38, 39, which, at their outer ends, are connected to a relatively rigid hoop member 40 which joins the outer combustor liner 20. The inner ends of the sheet metal plates 38 and 39 are joined together as by welding to thus form the downstream end of a curved annular chamber 42.

A sheet metal band 44 is secured to the inner end of the outer plate 38, as by welding, and extends toward the compressor a short distance, where it is joined to a flanged sheet metal disc 46. The inner portion of the disc 46 is secured to a frame member 48, which is an integral component of the nozzle diaphragm 32. Bolts 49 secure this assembly as well as securing the nozzle frame 48 to an engine frame 50.

A small gap is provided between the compressor passageway 14 and the hoop 40 to permit relatively cool compressor discharge air to flow into a chamber 52 (See also FIG. 1) between the curl member 30 and the surrounding structure of the engine. This cooling air then flows through a series of holes 54, see FIG. 4 also, spaced around the outer curl plate 38, adjacent the hoop 40 and is then discharged through holes 55 formed in the plate 39 adjacent the nozzle diaphragm 32.

The cooling air thus passes through chamber 42 flowing over substantially the entire surface of the inner plate 39. The air employed in cooling the curl member 30 and particularly its inner plate 39 is then returned to the motive fluid stream generated by the engine. The energy of the cooling air is thus at least partially recovered to minimize losses in overall engine cycle efficiency.

Due to the temperature differentials between the inner and outer curl plates, there is a tendency for these members to be forced towards each other and close off the chamber 42. A minimum chamber dimension is maintained at all times by dimples 56, preferably formed in the outer plate 38, which maintains at least a minimum spaced relationship between the plates 38 and 39.

Further recognition of the temperature differentials and the resultant differences in thermal growth of the inner and outer plates is found in the described mounting of the inner end of the curl member. The relatively thin sheet metal band 44 and flange 46 provide a flexible bracket arrangement which permits limited relative movement between the inner end of the curl member and the nozzle diaphragm frame. This relative movement, which may be in both radial and axial directions, may be further guided by dimples 58 formed on the outer plate 38. These dimples normally ride on a flange surface 60 of the diaphragm member and provide a limited surface engagement therebetween.

Referencing next FIG. 3, a modified curl member 30' is illustrated. Except for the curl member itself, all other components of the compressor remain the same and identified by like reference characters as previously used. Again, the curl member 30' comprises inner and outer plates 62 and 64 in the form of curved annular shells. These plates are mounted in the same fashion with respect to the hoop 40 and nozzle frame 48. The difference in the present curl member is found in the provision of an intermediate sheet metal plate 66 which is secured, as by welding, at its outer or upstream end to the outer plate 62, adjacent the hoop 40. The intermediate plate 66 is also annularly curved and extends towards and terminates adjacent the downstream, or inner, end of the curl member 30' where the plates 62 and 64 are joined. Thus two chambers 70 and 72 are defined within the curl member 30'. These chambers join together at the termination of the intermediate plate 66 at the inner end of the curl member.

Cooling air enters the outer chamber 70 through holes 74, formed in plate 62, opening into the chamber 52 which is pressurized by compressor discharge air as before. Cooling air enters the inner chamber 72 through holes also formed in the outer plate 62. The spent cooling air from both chambers is then discharged into the hot gas stream through holes 82.

This arrangement provides two simultaneous flows of cooling air through the curl member 30 which respectively cool the plates 64 and 66. By cooling the plate 66, a greater degree of effectiveness may be obtained in cooling the plate 64 which is directly exposed to the hot gas stream. By properly controlling the size and number of the holes 74 and 80 it is possible to attain a high degree of cooling effectiveness utilizing a minimum mass flow of cooling air.

Again, the cooling flow chambers are controlled, as to their minimum dimensions, by a dimple arrangement. This time dimples 76 are formed in the intermediate plate and extend in opposite directions to respectively engage the inner and outer plates 62 and 64. Alternatively, some of the dimples could also be formed in the outer plate 62 to space the intermediate plate 66 therefrom.

Differences in thermal expansion are further recognized in the fact that only the outer end of the intermediate plate 66 is anchored while the inner end is free to float. Further, the inner plate is a non-structural member and therefore is preferably relatively thin to minimize both stresses and weight.

The present invention has been described in connection with a gas turbine engine incorporating a reverse flow combustor, to point out the more specific aspects of the invention. However, in the broader aspects of the invention, it will be recognized that there is provided an improved cooling construction for duct wall members which define the flow path for a hot gas stream. The spirit and scope of the present inventive concepts is therefor to be derived solely from the following claims.

Having thus described the invention what is claimed is novel and desired to be secured by letters patent of the United States is:

In a gas turbine engine a duct wall for defining, at

least in part, the flow path of a hot gas stream generated by a combustor, said duct wall comprising:

first and second plates, said plates being spaced apart to thereby define a relatively thin chamber therebetween, said first plate being adapted for direct exposure to the hot gas stream from said combustor;

means for introducing cooling air into one end of said chamber means, flowing the cooling air through said chamber means and over substantially the entire surface area of said first plate, said plates including passages extending from said chamber to the hot gas stream for discharging the cooling air from said chamber;

an intermediate plate provided between said first and the intermediate plate is closely spaced from both the first and second plates and separates said first and second chambers at said one end of the chamber means and terminates short of the other end of the chamber means thereby allowing communication between said first and second chambers thereat,

the cooling air means includes separate passageways at said one end of the chamber means for respectively introducing cooling air into said first and second chambers, and passageways at the other end of said chamber means, which extend through said first plate for discharge of the spent cooling air from both the first and second chambers, into the hot fluid stream, and

the spacing means include dimples formed on said intermediate plate which are engageable with at least the first plate to maintain a minimum spacing therebetween.

3. A duct wall as in claim 2 wherein said plates are curved to provide controlled cooling of the first plate as it turns the flow direction of the hot fluid stream to which it is exposed.

4. A reverse flow combustor comprising:

pair of annular, spaced liners defining, therebetween, an annular combustion zone,

means for introducing fuel into one end of said liners for combustion with pressurized air introduced into said combustion zone,

inner and outer curl members respectively extending from said inner and outer liners and defining an annular flow path for the hot gas stream, generated in the combustion zone, which is curved inwardly through approximately to discharge the hot gas stream into a turbine,

said outer curl member including first and second annular substantially coextensive plates, said plates being spaced apart and secured to one another at their upstream and downstream ends to thereby define a single relatively thin chamber therebetween, said first plate being directly exposed to the hot gas stream flowing from the combustion zone and turning it inwardly towards said turbine,

means for introducing pressurized cooling air into the upstream (relative to the flow direction of the hot gas stream) end of the chamber means, flowing the cooling air through said chamber means and over substantially the entire surface area of siid first plate, said means including passages discharging the spent cooling air from said chamber means, adjacent the downstream end of the curl member, into said hot gas stream, and

a plurality of imperforate dimples, formed on the second plate, extending into said chamber and engageable with said first plate for maintaining a minimum flowpath area through said chamber means to thus assure a desired flow of cooling air.

5. A reverse flow combustor as in claim 4 further comprising:

a relatively rigid hoop member to which the first and second plates are secured at their upstream ends thereby closing the chamber at its upstream ends,

a relatively fixed member, and

a flexible, resilient bracket secured to the downstream end of one of said plates and adapted for attachment at its outer end to said relatively fixed member.

6. A reverse flow combustor as in claim 5 wherein:

said relatively fixed member is a flange of a turbine nozzle disphragm,

the flexible bracket comprises a sheet metal band secured at one end to said second plate and having an inwardly extending disc flange from the other end of the band, the inner portions of the disc flange being adapted for attachment to the flange of said turbine nozzle diaphragm, and

further wherein the outer surface of the second plate has dimples formed thereon at its downstream end, said dimples being angularly spaced and providing limited sliding engagement with a circumferential surface of the nozzle diaphragm to thus guide the curl member for relative movement with respect to the fixed nozzle diaphragm.

Po-ww UNITED STATES PATEN" OFFICE CERTIFICATE OF CORRECTION pa t 3 ,844;ll6 Dated October 29, 1974 Inventefle) LAWRENCE R. MA'ITO It is certified that errbr appears in the above-identified patent and that said Lettets Patent are hereby corrected as shown below:

Col. 1, line 12', "high" should read "light".

Col. 2 line 21, "lines" should read lihers".

Col. 6', line 1 6, "si id sfiould ead d j.

signed and sealed this-24th day of December 1974.

- MCCOY r1. GIBSON JR. I-IARSHALL DANN L- a in Uffi'Qer' 4 Comm ssioner of Patents 

1. In a gas turbine engine a duct wall for defining, at least in part, the flow path of a hot gas stream generated by a combustor, said duct wall comprising: first and second plates, said plates being spaced apart to thereby define a relatively thin chamber therebetween, said first plate being adapted for direct exposure to the hot gas stream from said combustor; means for introducing cooling air into one end of said chamber means, flowing the cooling air through said chamber means and over substantially the entire surface area of said first plate, said plates including passages extending from said chamber to the hot gas stream for discharging the cooling air from said chambEr; an intermediate plate provided between said first and second plates and in spaced relation to both of said plates to thereby define first and second chambers; and a plurality of spacing means effective between said intermediate plate and both said first and second plates to maintain a minimum flow path area through both the first and second chambers.
 2. A duct wall as in claim 1 wherein the intermediate plate is closely spaced from both the first and second plates and separates said first and second chambers at said one end of the chamber means and terminates short of the other end of the chamber means thereby allowing communication between said first and second chambers thereat, the cooling air means includes separate passageways at said one end of the chamber means for respectively introducing cooling air into said first and second chambers, and passageways at the other end of said chamber means, which extend through said first plate for discharge of the spent cooling air from both the first and second chambers, into the hot fluid stream, and the spacing means include dimples formed on said intermediate plate which are engageable with at least the first plate to maintain a minimum spacing therebetween.
 3. A duct wall as in claim 2 wherein said plates are curved to provide controlled cooling of the first plate as it turns the flow direction of the hot fluid stream to which it is exposed.
 4. A reverse flow combustor comprising: a pair of annular, spaced liners defining, therebetween, an annular combustion zone, means for introducing fuel into one end of said liners for combustion with pressurized air introduced into said combustion zone, inner and outer curl members respectively extending from said inner and outer liners and defining an annular flow path for the hot gas stream, generated in the combustion zone, which is curved inwardly through approximately 180* to discharge the hot gas stream into a turbine, said outer curl member including first and second annular substantially coextensive plates, said plates being spaced apart and secured to one another at their upstream and downstream ends to thereby define a single relatively thin chamber therebetween, said first plate being directly exposed to the hot gas stream flowing from the combustion zone and turning it inwardly towards said turbine, means for introducing pressurized cooling air into the upstream (relative to the flow direction of the hot gas stream) end of the chamber means, flowing the cooling air through said chamber means and over substantially the entire surface area of siid first plate, said means including passages discharging the spent cooling air from said chamber means, adjacent the downstream end of the curl member, into said hot gas stream, and a plurality of imperforate dimples, formed on the second plate, extending into said chamber and engageable with said first plate for maintaining a minimum flowpath area through said chamber means to thus assure a desired flow of cooling air.
 5. A reverse flow combustor as in claim 4 further comprising: a relatively rigid hoop member to which the first and second plates are secured at their upstream ends thereby closing the chamber at its upstream ends, a relatively fixed member, and a flexible, resilient bracket secured to the downstream end of one of said plates and adapted for attachment at its outer end to said relatively fixed member.
 6. A reverse flow combustor as in claim 5 wherein: said relatively fixed member is a flange of a turbine nozzle disphragm, the flexible bracket comprises a sheet metal band secured at one end to said second plate and having an inwardly extending disc flange from the other end of the band, the inner portions of the disc flange being adapted for attachment to the flange of said turbine nozzle diaphragm, and further wherein the outer surface of the second plate has dimples formed thereon At its downstream end, said dimples being angularly spaced and providing limited sliding engagement with a circumferential surface of the nozzle diaphragm to thus guide the curl member for relative movement with respect to the fixed nozzle diaphragm. 